Generation of a NanoDLP Mask for the Wanhao D7

Update as of 17/9/2017:  This is a very flawed article as I confess in a later post here.  Flawed, yet because the D7 UV light is distributed so heavily to the center, it still worked well!  Sorry for any confusion and that I did not post this confession sooner (though I did make a note on the 14th)!

I finally decided to invest the effort in creating masks so that my build plate is evenly exposed to radiation from the UV LED Array of the Wanhao D7 3D Printer.    The annotation on the following images explains the process.  Links are at the bottom.

Note that as of 14:53 on 7/9/2017 I am chasing a little bit of under cure on the edges even with the measurements.  Things are much, much better than without the mask, just not perfect!

Note that as of as of 16:24 on 14/9/2017 I need to 'fess up that my understanding of how mask generation works in NanoDLP was pretty flawed below.  Stay tuned.

Created a printable grid that matches the default grid on the NanoDLP mask generator (e.g. 10 columns by 5 rows).  The tabs can be used to secure the grid.  Theoretically the one without tabs could be printed on the D7.  The camera adapter was my first plan but the iPhone light meter app I tried could not detect the UV well enough.  The little square thing is a mount for the photoresistor that I ended up using.

Ultra simple Arduino circuit.  Photoresistor to ground and to A5 with a 10k resistor to +5v.  Read A5 averaging 2 seconds of inputs 100ms delayed from each other (20 in other words) and display the result.

Printed matrix secured to the printer with the photoresistor in a cell.

Top right is the output from the Arduino.  Bottom right is the monitor built into the printer.  Left is the spreadsheet that I used to calculate the mask values.

View of the completed spreadsheet.  Layer cure time will need to be increased by the stated percentage.

The above spreadsheet also has tables for subsets of the build platform.  This one only uses two fifths of the build plate and as such only increases cure time by 11%.  The white area of the first table is the printable area to model.  On the second table the yellowish cells represent unprintable but the light grey ones are adjustable to be useable.

Mask as generated.  Located in ~/printer/public/plates on the NanoDLP instance.

Proof is in the pudding.

Grid on Thingiverse
Arduino Sketch
NanoDlp Mask Calculator
Link to Mask - Use at your own risk!

Parts needed for your own measuring device:

1. Photoresistor -  Search for "5516 Photoresistor Sensor Detection Light Dependent Resistor". Interestingly I did not buy this for UV sensitivity but it works fine and I wonder if other photoresistors might as well.  If you are reading a difference of more than 30-40% from the middle to the edges of your display it might be the photoresistor.
2. 10K Resistor - Used for the other leg of a classic voltage divider.  
3. Arduino Uno - Search for them on eBay.  You can get clones from China for a couple of quid if you are patient with shipping times.

Comparison of masks for my two printers.

Interestingly the printer on the left has a glass plate behind the LCD and the one on the right does not.

Here is the test piece from my second printer.  Same issue with measuring the little pointy things...there is a slight under cure at the edges.

Calibration pieces from printer #1.  First time anything has stuck to that corner!

Closeup of the above calibration pieces.  Can you tell which one was center, versus side, versus corner?